The present invention relates to semiconductor devices, and more particularly to semiconductor devices containing both an analog circuit such as an analog radio frequency (RF) circuit and a digital circuit.
In recent years, large-scale systems on chip (SoCs) containing an analog RF circuit have been increasingly implemented in order to reduce the cost and size of radio modules. However, in the SoCs containing an analog RF circuit, noise that is generated by the digital circuit is introduced into the analog RF circuit through a semiconductor substrate, which contributes to performance degradation of the analog RF circuit. In such semiconductor devices, sufficient isolation needs to be provided between a digital circuit portion and an analog RF circuit portion to remove signal interference between blocks as much as possible. Note that this problem can also occur even when an analog circuit other than the analog RF circuit is contained together with the digital circuit.
Related art for such element isolation that has been reported to ensure isolation includes techniques of noise removal by guard rings, trench isolation, increased substrate resistance, etc.
The noise removal by guard rings is described in, e.g., Japanese Patent Publication No. H03-46335. In a semiconductor device of Japanese Patent Publication No. H03-46335, noise is blocked in a blocking region, which is formed by a substrate contact diffusion region provided around a digital circuit as a noise source and metal interconnects connected thereto. Since the metal interconnects are grounded, noise propagating through a substrate can be absorbed by the metal interconnects.
The trench isolation is described in Japanese Patent Publication No. 2007-67012 and Japanese Patent No. 3159237. In semiconductor devices described in Japanese Patent Publication No. 2007-67012 and Japanese Patent No. 3159237, a trench type insulating region is formed to surround a semiconductor element, thereby reducing propagation of signals or noise that is caused by the signals.
Another method is to increase the resistivity of a silicon substrate to form a high resistivity region around a semiconductor element in the substrate, thereby attenuating signals that leak from the semiconductor element and propagate through the substrate, and reducing crosstalk.